Vodafone on the Gürzenich

So there actually are a lot of 900 only Vodafone sites left even inside the metro area? I figured that at least all sites would have 1800 on them, and more and more sites UMTS??

No, most are either GSM 900 only or GSM 900/UMTS 2100 setups. Vodafone has GSM 1800 backup sites in other areas. Wolfgang Duven's Senderliste has them marked in red in the Cell ID row:

http://www.duven.de/d2sender/d2k.htm